Reactive Extrusion Printing for Simultaneous Crystallization‐Deposition of Metal–Organic Framework Films

Abstract Reactive extrusion printing (REP) is demonstrated as an approach to simultaneously crystallize and deposit films of the metal–organic framework (MOF) Cu3btc2 (btc=1,3,5‐benzenetricarboxylate), also known as HKUST‐1. The technique co‐delivers inks of the copper(II) acetate and H3btc starting materials directly on‐surface and on‐location for rapid nucleation into films at room temperature. The films were analyzed using PXRD, profilometry, SEM and thermal analysis techniques and confirmed high‐quality Cu3btc2 films are produced in low‐dispersity interconnected nanoparticulate form. The porosity was examined using gas adsorption which showed REP gives Cu3btc2 films with open interconnected pore structures, demonstrating the method bestows features that traditional synthesis does not. REP is a technique that opens the field to time‐efficient large‐scale fabrication of MOF interfaces and should find use in a wide variety of coating application settings.


Materials and Methods
Trimesic acid (H3btc) was purchased and used as received from Sigma-Aldrich and copper(II) acetate monohydrate (Cu(OAc)2·H2O)was purchased and used as received from Fluka.
Extrusion printing was carried out using a Sheline 1820 Machinery printer. The stage and printer head system, and the extrusion deposition system, were controlled by Link CNC-EMC software. The stage and the printer head were movable in X Y and Z direction. The substrate was moved at a speed of 193 mm/min in the longitudinal and lateral directions (X Y motion). The gap between the nozzles and the substrate (Z motion) was adjusted manually to 0.5 mm and constant for all printing experiments.
Disposable syringes (1.00 mL) were used as ink reservoirs. Stainless steel needles were used as nozzles (22 GE). One nozzle extruded the copper salt ink and the other extruded the H3BTC solution at the same time. The flow speeds of the reactive inks were controlled at speed 6 μm/s and the volume of ink flow rate from the syringes (1.00 mL) was 0.104 mL/s. After reactive printing, the formed film was washed twice with EtOH and twice with acetone and then dried at room temperature, unless stated otherwise.
Glass microscope slides (76.2 × 25.4 mm) were used as substrates. O2 Plasma treatment was done using a Harrick plasma system PDC002for 3, 6, 9, or 12 minutes with a chamber pressure set at 1000 milliTorr. A CAST3 USA KINO goniometer was used to measure contact angles and surface tensions.
Values were obtained from measurements of five different drops for each surface and ink. The sessile drop method was used for measuring contact angle, and the pendant drop method was used for measuring surface tension at room temperature. Ink droplets were dispensed on to the substrate by the printer and software program for recording and analysing contact angle and surface tension.
Optical micrographs were recorded using a Leica M205A or a Leica DM6000 each fitted with CCD cameras. The Leica M205A was used at scales from 1-10 mm and the Leica DM6000 from 500-25 μm. A JEOL JSM-7500 was used to study morphologies of all the samples at 15 keV.
A GBC Multi Materials Analyser X-ray diffractometer was used to record patterns of printed MOF films. Data were recorded in the 2θ range of (5-30°) with a step size of 0.05 at 1°min -1 . Patterns were recorded directly on the surface they were printed on.
TGA-DSC was performed using NETZSCH STA 449F3 Jupiter simultaneous analyser, connected to a multi-channel temperature controller (TR 004). Typically, ~8 mg of the sample was heated from 25 to 1000 ˚C at 10 ˚C per min under N2/ O2 flow (20 cm 3 min -1 ). The data analysis was recorded and carried out on the NETZSCH Proteus version 6.1.0 software system. Gas adsorption studies were carried out at the Wollongong Isotope and Geochronology Laboratory using a Quantachrome Autosorb MP instrument and high purity nitrogen (99.999 %) gas. Surface areas were determined using Brunauer-Emmett-Teller (BET) calculations.
The image-J64-bit software program was used to measure the distribution and the particles size of SEM images. The SEM image was imported then processed by re-setting the scale of the software based on the scale of SEM image. Then 100 particles were selected randomly, and their diameters were measured manually.             Figure S10.
XPS Discussion: We compared samples from our reactive extrusion printing to a literature method. We found extensive reduction of copper(II) to copper(I) using Al Kα radiation (1486.6 eV) at 70 W with 50 eV pass energy with ~20 scans. Reducing the pass energy to 20 eV (same step size of 0.1 eV) and reducing the number of scans gave good results and this is the data presented. The samples produced by reactive extrusion printing showed no presence of copper(I), which has been used as a marker of defects. 2 This has to be used with caution as we demonstrate above that increasing X-ray exposure time increases the proportion of copper(II) photoreduction for Cu3btc2 samples with defects, even with low dose X-rays.